Insulating inorganic metal oxide materials, such as ferroelectric materials or perovskite material, have high dielectric constants and low leakage current which make them attractive as cell dielectric materials for high density DRAMs and non-volatile memories. Perovskite material and other ferroelectric materials exhibit a number of unique and interesting properties. One such property of a ferroelectric material is that it possesses a spontaneous polarization that can be reversed by an applied electric field. Specifically, these materials have a characteristic temperature, commonly referred to as the transition temperature, at which the material makes a structural phase change from a polar phase (ferroelectric) to a non-polar phase, typically called the paraelectric phase.
Despite the advantages of high dielectric constants and low leakage, insulating inorganic metal oxide materials suffer from many drawbacks. For example, all of these materials may incorporate oxygen or are otherwise exposed to oxygen for densification to produce the desired capacitor dielectric layer. Unfortunately, the provision of such layers or subjecting such layers to oxidation densification also undesirably oxidizes the underlying bottom or lower storage node plate, which is typically conductively doped polysilicon. The art accepted solution to this problem is to provide an intervening oxidation barrier layer between the underlying conductive polysilicon and overlying insulating inorganic metal oxide dielectric layer. This layer must accordingly be electrically conductive, as the underlying polysilicon must be in electrical connection with the insulating inorganic metal oxide dielectric layer.
Unfortunately, there are a limited number of oxidation barrier materials which are conductive. Elemental platinum (a conductive oxidation barrier) on polysilicon has been suggested as a composite layer or construction for a lower capacitor plate, but undergoes physical degradation with thermal cycling due to silicon diffusion through the platinum. Sputtered TiN and CVD TiN (other conductive barriers) have been known to fail due to diffusion along grain boundaries.
It would be desirable to overcome some of these prior art drawbacks in developing a method and capacitor construction which enables utilization of insulating inorganic metal oxide materials as capacitor dielectric layers.